A Highly Sensitive and Selective Spectrofluorimetric Method for The

American Journal of Analytical Chemistry, 2019, 10, 316-347 http://www.scirp.org/journal/ajac ISSN Online: 2156-8278 ISSN Print: 2156-8251 A Highly Sensitive and Selective Spectrofluorimetric Method for the Determination of Arsenic at Pico-Trace Levels in Some Groundwater, Real, Environmental, Biological, Food and Soil Samples Using 2-(α-Pyridyl)-Thioquinaldinamide M. Jamaluddin Ahmed1*, Ayesha Afrin1,2, Mamunur Rashid1 1Laboratory of Analytical Chemistry, Department of Chemistry, University of Chittagong, Chittagong, Bangladesh 2Department of Applied Chemistry and Chemical Engineering, University of Chittagong, Chittagong, Bangladesh How to cite this paper: Ahmed, M.J., Afrin, Abstract A. and Rashid, M. (2019) A Highly Sensitive and Selective Spectrofluorimetric Method for A very simple, ultra-sensitive, highly selective and non-extractive new spec- the Determination of Arsenic at Pico-Trace trofluorimetric method for the determination of arsenic at pico-trace levels Levels in Some Groundwater, Real, Envi- using 2-(α-pyridyl)-thioquinaldinamide (PTQA) has been developed. PTQA ronmental, Biological, Food and Soil Samples Using 2-(α-Pyridyl)-Thioquinaldinamide. has been proposed as a new analytical reagent for the direct non-extractive American Journal of Analytical Chemistry, spectrofluorimetric determination of Arsenic (V). This novel fluorimetric rea- 10, 316-347. gent, PTQA becomes oxidized in a slightly acidic (0.025 - 0.1 M H2SO4) solu- https://doi.org/10.4236/ajac.2019.108023 tion with Arsenic (V) in absolute ethanol to produce highly fluorescent oxidized product (λex = 303 nm; λem = 365 nm). Constant and maximum fluo- Received: June 22, 2019 Accepted: August 18, 2019 rescence intensities were observed over a wide range of acidity (0.025 - 0.1 M Published: August 21, 2019 H2SO4) for the period between 2 min and 24 h. Linear calibration graphs were −1 −1 obtained for 0.001 - 800-μgL of As, having a detection limit of 0.1-ngL ; the Copyright © 2019 by author(s) and quantification limit of the reaction system was found to be 1-ngL−1 and the Scientific Research Publishing Inc. This work is licensed under the Creative RSD was 0% - 2%. A large excess of over 60 cations, anions and complexion Commons Attribution International agents (like, chloride, phosphate, azide, tartrate, oxalate, SCN, etc.) do not License (CC BY 4.0). interfere in the determination. The developed method was successfully used http://creativecommons.org/licenses/by/4.0/ in the determination of arsenic in several Certified Reference Materials (al- Open Access loys, steels, ores, human urine, hair, nails, bovine liver and sediments) as well as in some biological fluids (human blood, urine, hair, nail and milk), soil samples, food samples (vegetables, fruits, rice, corn and wheat), solutions con- taining both arsenic (III) and arsenic (V) speciation and complex synthetic mixtures. The results of the proposed method for assessing biological, food DOI: 10.4236/ajac.2019.108023 Aug. 21, 2019 316 American Journal of Analytical Chemistry M. J. Ahmed et al. and soil samples were comparable with both ICP-OES & AHG-AAS and were found to be in excellent agreement. Keywords Spectrofluorimetry, Arsenic Determination, Groundwater, 2-(α-Pyridyl)-thioquinaldinamide, Environmental, Biological, Soil, Food Samples 1. Introduction The word “Arsenicosis” is unknown to the general people even a few days ago. But now-a-days maximum people of Bangladesh came to know from different sources that they have been suffering from a serious disease which is not due to virus but is metallic, the name of this metalloid is arsenic [1]. In October 1997, a survey conducted by Dhaka Community Hospital identified arsenic contamination in 59 districts where 60 million people are at risk. The water of shallow tube-wells in 59 districts showed arsenic contamination above 50 μgL−1 (BSTI standard). According to the latest statistics of 64 districts of Bangladesh 61 districts contain arsenic [2] that one fifth of the population of our country is living on the edge [2], being exposed to arsenic contamination (WHO tolerance limit is 10 μgL−1). However, all the investigations and studies signal arsenic contamination in groundwater of Bangladesh as “Disaster” [3]. The determination of arsenic (III) and arsenic (V) in environmental and biological systems is of considerable current interest because the toxicity of this element to aquatic and terrestrial organism including humans depends on its oxidation state [4]. Arsenic (V) is considered to be essential to mammals for the main- tenance of growth, blood cells and normal iron metabolism [5], but arsenic (III) is reported to be toxic because of its complexation with coenzymes, coagulation of proteins and uncoupling of phosphorylation and its adverse impact on skin, liver, nose and throat [5]. Strong evidences were provided to indicate that arsenic in drinking water was responsible to cause skin, lung and bladder cancer [5]. Groundwater is the preferred source of drinking water for 99% people in the ru- ral areas of Bangladesh. The provisional WHO guideline value of arsenic for drinking water is 10-μgL−1. Therefore, extremely low concentrations of arsenic in groundwater used for potable and domestic purposes should be known accu- rately [3]. Hence, reliable methods are needed to check the arsenic status of a human and to monitor the occupational exposure to this element by measuring its concentration in bodily fluids. In the expanding analytical fields such as environmental, biological and ma- terial monitoring of trace metals, there is an increasing need to develop simple, sensitive and selective analytical techniques that don’t use expensive or compli- cated test equipment. Many sophisticated techniques, such as NAA, X-ray fluorescence, pulse polarography, ICP-OES, ICP-MS, GF-AAS, AHG-AAS and spec- trophotometry have been used widely to the determination of arsenic. The first DOI: 10.4236/ajac.2019.108023 317 American Journal of Analytical Chemistry M. J. Ahmed et al. four methods are disadvantageous in terms of cost and the instruments used in routine analysis. GF-AAS is often lacking in sensitivity due to sublimation at high temperature, AHG-AAS is sensitive but often affected by matrix conditions of samples such as salinity. There is no direct spectrophotometric method for the determination of arsenic. Only one solvent extractive method is considered as standard method which uses Ag-diethyldithiocarbamate (Ag-DDTC) is very less sensitive [6]. ADDC is also insoluble in water but soluble in organic solvents such as pyridine and chloroform which are themselves carcinogenic according to EPA [7]. Spectrofluorimetry is essentially an ultra-trace analysis technique and is one of the most powerful and successful tools in chemical analysis. Spectrofluo- rimetry is extremely sensitive so much so that sometimes femtogram (10−15 g∙g−1) per gram level or less can be determined [8]. The goal of the present work was to develop a simpler direct spectrofluorimetric method for the pico-trace determination of arsenic. In the search for a more sensitive reagent, in this work a new reagent was synthesized according to the method of Porter [9] and an oxidation reaction of 2-(α-pyridyl)-thioquinaldinamide (PTQA); with As(V) and forms an intensely fluorescent oxidized product. Al- though PTQA has been reported to be spectrofluorimetric reagent for Cr(VI) [10], Se(IV) [11] and Mn(VII) [8] but has not previously been used for the spectrofluorimetric determination of arsenic. The method possesses distinct advan- tages over existing methods [12]-[32] with respect to sensitivity, selectivity, range of determination, simplicity, speed, pH/acidity range, thermal stability, accuracy, precision and ease of operation. The method is based on the oxidative reaction of non-fluorescent PTQA in a slightly acidic (0.025 - 0.1 M H2SO4) solution with As(V) in presence of ethanol to produce a highly fluorescent oxidized product, followed by a direct measurement of the fluorescence intensity in an aqueous solution at room temperature (25˚C ± 5˚C). Oxidation is very rapid, and no extraction is required. With suitable masking, the reaction can be made to be highly selective and the reagent blank solutions do not show any fluorescence. 2. Materials and Methods 2.1. Apparatus A Shimadzu (Kyoto, Japan) (Model-RF-5301PC) Spectrofluorophotometer with 1-cm quartz cells were used and a Jenway (England, UK) (Model-3010) pH me- ter with combination of electrodes were used for measurements of the fluorescence intensity and pH. The calibration and linearity of the instrument were frequently checked with standard quinine sulfate (10-mgL−1). A Shimadzu (Ja- pan) (Model: 9800) Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES), [λ = 418 nm, plasma gas flow rate (Lmin−1) = 15, LOD: 1 μgL−1 of As, RF Power (W) = 1400, Nebulizer gas flow rate (Lmin−1) = 1 - 10] and A Thermo Fisher Scientific (Model: ICE, origin USA) Atomic Absorption Spec- trophotometer equipped with a microcomputer controlled Automated Hydride DOI: 10.4236/ajac.2019.108023 318 American Journal of Analytical Chemistry M. J. Ahmed et al. Generation along with Flow Injection (AHG-AAS). The arsenic was determined at 197.3-nm. The Elemental Analyzer (Exeter Analytical Inc. Model: CE 440) equipped with supersensitive thermal conductivity detector for simultaneous determination of CHN was used. Infrared spectrum was recorded with a FTIR Spec- trophotometer, Shimadzu (Kyoto, Japan) (Model-IR Prestige 21, Detector DTGS KBr) in the range 7500 - 350 cm−1 and Model: JEOL 500SS, magnetic field strength: 500 MHz, solvent used: DMSO D6, standard: TMS, four channel NMR spectrometer with signal-to-noise ratio of 5000:1 for proton were used for characterization of the ligand. 2.2. Synthesis and Characterization of the Reagent 2.2.1. Synthesis of the Reagent 2-(α-pyridyl)-thioquinaldinamide (PTQA, C15H11N3S) (Molecular wt. = 265.18) was synthesized according to the method of Porter [9].

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